The present invention is directed to an atherectomy catheter, particularly, an atherectomy catheter including a positive displacement drive hydraulic motor.
Many technological advancements have been made in recent years for treatment of coronary disease. Surgical bypass techniques such as cardiopulmonary bypass surgery is routinely performed and is highly successful. While the risks of bypass surgery have been minimized through technological advancements, opening of the chest cavity is required. This requires special surgical skills and equipment which are not readily available in many areas. In many patients, a bypass operation may not be indicated and therefore various surgical techniques have been devised to treat occlusive coronary artery disease of such patients. For example, various prior art devices have been developed for removing and/or compressing atherosclerotic plaque, thromboses, stenoses, occlusions, clots, embolic material, etc. from veins, arteries, and the like. One such device is disclosed in U.S. Pat. No. 4,650,466 (Luther). Luther discloses an angioplasty device comprising a woven tube of metal or plastic fibers and a retraction stylet that are attached at one end of a catheter tube for insertion into a vein, artery and the like for the removal of plaque and similar material. One or more guide wires are attached to the woven tube for rotation and manipulation inside the artery. The woven tube is placed within the artery and expanded to contact the interior, plaque coated wall of the artery. Movement of the expanded woven tube abrades the plaque from the arterial wall to form particles which are trapped within the woven tubes. Removal of the angioplasty device from the artery removes the trapped plaque particles from the patient.
Other prior art devices include catheters fitted with an inflatable balloon for compressing occlusive materials such as plaque against the vessel wall. U.S. Pat. No. 4,273,128 (Lary) discloses a coronary cutting and dilating instrument for treatment of stenotic and occlusive coronary artery disease. The instrument disclosed therein includes a cutting and dilating instrument having one or more radially extending knife blades at a forward end thereof for making the coronary incision and an inflatable balloon for dilating the stenotic artery zone immediately after the incision.
Other angioplasty devices include a catheter having a motor driven cutting head mounted at its distal end. The cutting head is connected to the drive motor via a flexible drive shaft extending through the catheter. Extremely high rotational cutting head speeds have been achieved, in the range of two to three hundred thousand rpm, by these motor driven cutter heads. Various problems, however, have been associated with the use of balloon tipped catheters and high speed cutting heads. The balloon catheter is expanded by injection of pressurized fluid into the balloon to expand it against the wall of the artery. Some problems which have been reported include vessel dissection, perforation, rupture, conversion of a stenosis to an occlusion and embolization. Furthermore, angioplasty devices utilizing balloons do not remove the plaque from the arterial wall but simply compress the plaque against the wall of the vessel. Thus, the stenosis or occlusion frequently reoccur requiring further treatment.
Atherectomy devices utilizing motor driven high speed cutting head include a number of disadvantages. Heat dissipation and vibration is a problem. The path to the occlusion in an artery is often a tortuous path and therefore the flexible drive shaft connected to the cutter head must often traverse a number of bends or curves. Consequently, as the flexible drive shaft rotates, it contacts the inner wall of the catheter resulting in localized heating and vibrations due to the frictional contact. This, of course, is very uncomfortable for the patient and may result in weakening or perforation of the vessel.
It is therefore an object of the invention to provide an atherectomy catheter having a rotary cutter head at the distal end thereof driven by a positive displacement hydraulic motor.
It is another object of the invention to provide an atherectomy catheter having a relatively low speed cutter head powered by a high torque motor.
It is yet another object of the invention to provide an atherectomy catheter including a return passage for evacuating plaque and tissue removed by the cutting element.